The invention concerns an optical arrangement for the spectral fanning out of a light beam, preferably in the detection beam path of a confocal microscope, especially for the subsequent splitting of the fanned out beam out of its dispersion plane and for the detection of the split up spectral ranges, whereby the incoming light beam is focused on a pinhole.
Optical arrangements of the type in question here have been known from practice for a fairly long time, and specifically in connection with the simultaneous detection of several spectral ranges of a light beam, which is done with a stalled multi-band detector. A multi-band detector of this type makes for a complex optical arrangement that prior to this, with additional optics, has enabled multiple focusing.
If in the detection beam path of a confocal microscope one wants first to fan out the beam spectrally and then split it up out of its dispersion plane into individual spectral ranges, a high dynamic response for the separation of the excitation light is desired. However, diffractions that stem from the shape of the detection pinhole stand fundamentally in opposition to such a high dynamic, whereby in particular secondary maxima of the diffraction function in the spectrally separated detection range cause problems.
The object of the invention is therefore to configure and further develop an optical arrangement of the type in question such that a splitting of the fanned out beam with a suppression of interfering diffraction portions in the spectral range is possible.
The optical arrangement of the type in question according to the invention fulfills the aforementioned purpose by means of a pinhole having, a polygonal passageway for the light beam.
According to the invention, first of all it has been recognized that the form of the pinhole is responsible for the diffraction pattern that occurs for the various colors in the focus plane, or in the dispersion plane. While specifically a pinhole with a round passageway has annular secondary maximum diffraction values with limited dynamic response because of the diffraction effect occurring here, by using a pinhole with a polygonal passageway a completely different diffraction pattern results, namely a diffraction pattern whose secondary maximum diffraction values are arranged in lines that cross each other. In any case it is possible, in light of such an arrangement, to detect the primary diffraction maxima and to suppress the problematic secondary diffraction phenomena.
With regard to a concrete configuration of the pinhole or of the passageway formed there, it is of further benefit if thisxe2x80x94polygonalxe2x80x94passageway is configured symmetrically. In this case the passageway could be of triangular or four-cornered configuration, whereby in the context of a four-cornered configuration the symmetricalxe2x80x94and therefore rectangularxe2x80x94form is especially advantageous. From this there results specifically a completely specialized diffraction pattern of the pinhole for various spectral ranges or colors, namely a spectral cross, whereby the axes of the cross meet in the secondary diffraction maxima Secondary diffraction maxima lying in between are less problematic in the detection or splitting.
Diaphragms that are preferably variable could also be arranged in the beam path in front of or behind the pinhole. These diaphragms are used to suppress diffraction maxima or diffraction phenomena of a higher order.
In principle simultaneous detection of several spectral ranges of a light beam is possible without additional measures if the light beam is first spectrally fanned out and then a splitting of the fanned out beam out of the dispersion plane is performed. The splitting of the fanned out beam out of the dispersion plane is accomplished by means of a special optical arrangement, whereby the partial beams split up into spectral ranges or the spectral ranges themselves are detected, and indeed are detected simultaneously. The important thing here is that a fanning out of the light beam precedes the actual splitting into spectral ranges so that the splitting out of the dispersion plane can occur on the fanned out beam. In any case a multiple focusing with additional optics is not necessary here.
In principle two optically arrangements are provided here, namely once for the spectral fanning out of the light beam and another time for splitting and subsequent detection. The pinhole on which the incoming lightbeam is focused is situated upstream of the arrangement for spectral fanning out of the light beam, whereby the pinhole can be situated directly downstream of a laser scanner. What is important here, in any case, is the recognition that the form of the passageway in the pinhole creates a specific diffraction pattern of the fanned out light beam in the dispersion plane.
From the pinhole, the beam in some cases runs through the previously mentioned variable diaphragm to focusing optics and dispersion means. The dispersion means can be designed as a prism for an especially simple construction. Focusing optics, which can in turn comprise a lens arrangement, are arranged both in front of and behind the dispersion means or prism.
The beam running divergent from the path from the pinhole to the prism is focused through the focusing optics into the gap/detector arrangement situated downstream at which point the splitting into spectral ranges occurs.
Regarding the gap/detector arrangement, it is advantageous if special color selection gaps are provided there in the focusing plane or dispersion plane of the fanned out beam, said color selection gaps being in turn arranged and aligned such that diffraction can be screened out at the detection gap.